Porous membranes are widely used in the filtration of particulate, ionic, microbial and other contaminants from fluids in pharmaceutical, microelectronics, chemical and food industries. In use, the membranes are formed into a device (e.g., pleated cartridge elements, hollow tubes, stack of flat disks, etc.) which is placed in the fluid stream to be filtered.
The trend towards narrower line widths in semiconductor manufacturing has placed an ever increasing burden on particulate contamination control in semiconductor fabrication. The trend to tighter filtration has led to the introduction of fluoropolymer filtration membranes, with a rated pore size as low as 10 nm. Despite the success of such membranes, there is a need for fluoropolymer membranes to maintain sufficient liquid permeability while realizing superior particle retention.
Known methods to improve the particle retention or decrease the pore rating of a fluoropolymer membrane include compressing the membrane by passing the membrane through the nip of two calendar rolls. While such compression causes densification of the membrane, thereby improving particle retention, the compressed membrane suffers a significant loss in liquid permeability thereby limiting its use as a filtration device.